This invention relates to an exhaust silencer for small internal combustion engines and particularly to an exhaust silencer employing multiple silencing stages.
Internal combustion engines are generally constructed with an exhaust silencer or muffler unit connected with the exhaust gas passageway. Various muffler constructions have been suggested to reduce the exhaust noises associated with internal combustion engines without affecting the performance of the engine. This is particularly true with small two-cycle engines employed in recreational vehicles such as snowmobiles and other off-road devices. The demand for improved noise reduction has increased with recent noise regulations and standards which are promulgated by various governmental organizations or units. Consequently, the provision of a highly efficient silencer has become increasingly important in the practical production and sale of such recreational vehicles.
Generally, the internal combustion engines are adapted to operate at a given revolution per minute and the exhaust system is generally provided with a power tuning pipe to maximize the efficiency of operation at normal operating RPM. The muffler is connected to the discharge end of the tuning pipe to significantly reduce the undesirable noise levels associated with such engines. A widely employed and satisfactory muffler which has been employed includes a small cylindrical member with an internal spiral duct lined with a suitable absorbing medium such as steel wool. The spiral chamber or housing is secured to the terminal end of the tuned exhaust pipe with the absorption characteristics such as to significantly reduce the noise output. The unit is reasonably small, compact and, thus, is adapted to recreational type vehicles. Absorptive muffler unit, however, attenuate the exhaust noise over a relatively narrow frequency range or spectrum and an undesirable and in some instances unacceptable noise level remains.
Theoretically, various control techniques employing intricate passageways can be readily constructed to further minimize the noise characteristic. However, many control techniques involves development of intricate passageways create increased back pressures in the exhaust system simultaneously with the noise reduction with an undesirable if not unacceptable reduction of power output of the engine. Long pipe and big volume resonators can also technically reduce the noise level and provide a theoretical solution. Long pipe and other large volumne resonators are not, therefore, particularly adapted to recreational vehicles because of the size and weight. Further, such designs generally include an significant cost factor which may prevent practical implementation.
Consequently, a significant demand exists in the silencer art particularly for two cycle engines employed in recreational vehicles for a small reliable, lightweight and inexpensive muffler silencer unit which produces the desired sound attenuation without unduly increasing of the exhaust back pressures or otherwise degrading engine operation.